1. Field of the Invention
The present invention relates to computer modeling a reservoir having faulted geologic horizons, and more particularly relates to a method, apparatus and computer program product for modeling such a reservoir having at least one reverse fault, and consequently having at least one multi-valued horizon.
2. Related Art
The energy industry is continuously involved with the exploration of underground deposits of hydrocarbons, such as oil and natural gas. In order to cost effectively locate and estimate the amount of hydrocarbon present in such deposits, as well as devise ways to recover them efficiently with the existing technology, the energy industry makes extensive use of computer modeling techniques.
Such modeling techniques are described in further detail in the following U.S. patents, which are hereby incorporated herein by reference into this specification:                1) U.S. Pat. No. 5,982,707, entitled “Method And Apparatus For Determining Geologic Relationships For Intersecting Faults”, granted Nov. 9, 1999, William E. Abbott.        2) U.S. Pat. No. 6,014,343, entitled “Automatic Non-Artificially Extended Fault Surface Based Horizon Modeling System”, granted Jan. 11, 2000, Graf et al.        3) U.S. Pat. No. 6,138,076, entitled “Automatic Non-Artificially Extended Fault Surface Based Horizon Modeling System”, granted Oct. 24, 2000, Graf et al.        
Earth formations typically include horizons and faults. It is well known that hydrocarbon deposits tend to be situated adjacent to intersections of these horizons and faults. Previously known modeling techniques were typically capable of handling normal faults but not reverse faults. For example, in a previous technique a reverse fault was treated as if it was a vertical fault, thereby eliminating overlapping horizon surfaces. However, such a simplification reduces the fidelity of the model and increases the error.
In another previously known solution, the hydrocarbon earth reservoir is partitioned into compartments, referred to as blocks, using all faults and artificially extending them to form closed partitioning of the reservoir. However, such techniques lead to unrealistic and complicated computer models thereby compromising the ability to understand the earth formation and derive accurate estimates of the hydrocarbon reserves. Dynamic Graphics' “EarthVision” uses this modeling approach, as an example.
In yet another previously known solution, the modeling technique requires the user to craft the reservoir model by hand. Technoguide's “Petrel” system or Roxar's “IRAP RMS” system uses this modeling technique, as an example. However, such techniques are tedious and time consuming. This technique tends to turn the human into an accessory to the computer by requiring users to interactively construct geometric models, rather than computing the models from the data. Additionally, these techniques are unable to effectively model reservoirs having compound faults.
From the above it should be appreciated that there is an increasing need to have a modeling technique that can handle various types of faults, including reverse faults, and be capable of producing realistic and accurate models. Additionally, it is desirable that the modeling technique support automation thereby requiring very little user interaction.